This invention relates to gas flow rate measurement and, more particularly, to a vortex generating mass flowmeter usable over a wide range of flow rates.
There are many different types of flowmeters in use today. One type, which is known as a vortex shedding flowmeter, generates intermittent, unstable vortices with a transversely elongated bluff body positioned in the flow stream passing through an unrestricted fluid line. The frequency of the intermittent vortices or perturbations is a measure of the flow rate through the fluid line, and this frequency is sensed to provide a flow rate reading. The devices are generally limited to liquid flow rate measurement due to the effect of compressibility of the gas on the vortex shedding process. A typical vortex shedding flowmeter is disclosed on Rodely U.S. Pat. No. 3,572,117, issued Mar. 23, 1971.
Another type of flowmeter measures the pressure difference across a calibrated orifice plate. In the case of gas measurement, due to compressibility effects, the mass flow rate is not only dependent upon the pressure difference but also temperature and density variations, and the relationship is nonlinear and highly complex. Thus, the measured pressure difference must be processed further to give a true reading of mass flow rate. These devices generally read gas flow over a limited range due to rapidly increasing pressure difference across the device.
My U.S. Pat. Nos. 4,240,293 and 4,372,169 disclose a flowmeter that utilizes the aerodynamic drag resulting from a bluff body to generate a pressure signal related to flow rate. The flowmeter comprises a flow passage in which a restriction is formed, a bluff body, in the form of one or more discs or truncated cones disposed on one side of the restriction, and a pressure sensor.